actually I was reading an interview JJ did and he thought the possibilites (in terms on # of shows) were endless. I mean, you have tons of back story to cover about the main characters and you can make new main guys because there are other people on the island besides the ones the show is currently focusing on. I mean, Alias has been on the same main plot (Some, including myself, would say "stuck" on the same plot) for 3 seasons now. I actaully stopped watching early last season, but my point is that this guy doesn't mind beating a dead horse. Tho thankfully he claims season 4 will be different, so maybe he is coming around.
BTW, originally the doctor was supposed to die in the pilot.